Due to present environmental concerns over the use of potentially ozone-depleting or flammable blowing agents, it is desirable to make styrenic polymer foam structures with aqueous blowing agents. Such foam structures made with aqueous blowing agents can be seen in U.S. Pat. No. 4,455,272, U.S. Pat. No. 4,559,367, and European Patent Application 89114160.8.
A problem with styrenic polymer foam structures made with aqueous blowing agents is the formation of bimodal cell structures of relatively larger primary foam cells and relatively smaller secondary foam cells. The bimodal cell structure makes machining and fabricating difficult since the smaller secondary cells govern mechanical properties. Easy machinability and fabricability of foam structures is important in decorative, floral, novelty, and craft applications as well as tongue and groove cutting.
It would be desirable to have a closed-cell, styrenic polymer foam structure blown with an aqueous blowing agent that is easy to machine and fabricate. It would be desirable to have such a foam structure with a unimodal or primary cell size distribution.